1. Field of the Invention
The present invention relates to a brake system for a vehicle, such as a four-wheel drive vehicle, an all-terrain vehicle (ATV), a side-by-side vehicle, and other types of vehicles, and more specifically, the present invention relates to a wet friction disk brake system incorporated in a rear reduction gear assembly in such a vehicle.
2. Description of the Related Art
FIGS. 1A and 1B illustrate a known ATV 101. The ATV 101 includes a body frame 102 formed mostly of pipe members assembled by welding. An engine 125 is mounted on a middle portion of the body frame 102. Front wheels 120 provided with low-pressure tires, i.e., balloon tires, are suspended from front right and front left portions of the body frame 102. Rear wheels 121 provided with low-pressure tires are suspended from rear right and rear left portions of the body frame 102. The rear wheels 121 are supported on rear end portions of a swing arm 129 pivotally joined to a rear lower end portion of the body frame 102 for swinging motion in a vertical plane and supported by a suspension system 132. The front wheels 120 are supported by right and left linkages 130 individually connected to a front lower end portion of the body frame 102 and supported by shock absorbers 133 so as to be able to swing in a vertical plane. The handlebar 122 is operated to control the front wheels 120 for steering.
As shown in FIG. 1A, the front wheels 120 and the rear wheels 121 are driven by a transmission including drive shafts, not shown, and differential gears 134 and 135 connected to the engine 125 and mounted on the body frame 102. A front carrier rack 131 is mounted on the front fender 107 and permits loading and supporting of baggage thereon from the front side of the ATV 101. Front fender 107 also encloses a pair of headlights 106, as shown in FIG. 1B. The front carrier rack 131, the handlebar 122, the fuel tank 124, and the seat 123 are arranged on the body frame 102 in that order from the front toward the rear of the body frame 102. A rear carrier rack 126 is located behind the seat 123 and is mounted on the rear fender 108.
The front wheels 120 are covered with the front fender 107. The rear wheels 121 are covered with the rear fender 108. A cover 109 is provided on the body frame 102 between the front fender 107 and the rear fender 108 so as to surround the fuel tank 124. Exhaust pipes 136 extend rearward from the exhaust ports of the cylinders of the engine 125 and are connected to the muffler 127.
A conventional assembly of a rear differential driving and braking system used in these types of vehicles is shown in FIG. 5 of U.S. Pat. No. 6,293,890, and includes a rear reduction gear assembly having a wet type multiplate braking system provided therein. FIGS. 1 and 2 of U.S. Pat. No. 6,293,890 show another vehicle including a wet type multiplate braking system provided in a rear gear case. In addition, the arrangements of the wet brake systems in the rear gear assemblies according to both types of structures described in U.S. Pat. No. 6,293,890 are very complicated, and do not allow for the combined wet brake and rear gear assembly to be located at various positions within the vehicle. This is partially due to the fact that the drive mechanisms used in these conventional vehicles are differential drive mechanisms and due to the fact that the wet type multiplate braking system is located on the input shaft of the rear gear, both of which facts cause significant limitations in the design freedom of locating and installing the combined wet brake and rear gear assembly at various positions in the vehicle. Also, these differential gear and braking systems are inefficient and may result in brake failure. As a result, the wet type multiplate braking system must be positioned at a very specific location within the vehicle which significantly limits the flexibility and design freedom of locating the combined wet brake system and rear gear case relative to the engine output and wheels of the vehicle.
U.S. Pat. No. 4,856,373 also teaches a conventional vehicle having a rear differential gear assembly including multiple brake disks. The rear differential gear assembly of U.S. Pat. No. 4,856,373 includes complicated differential gearing and a plurality of brake disks that must be mutually compressed to achieve braking. As a result, the combined wet brake and rear gear assembly in this conventional device can only be located at the rear wheel as seen in FIG. 2 of U.S. Pat. No. 4,856,373. Also, this conventional device suffers from the same disadvantages such as inefficient braking and complicated assembly as described above with respect to U.S. Pat. No. 6,293,890.
U.S. Patent Application Publication No. 2004/0040776 and U.S. Pat. No. 6,805,217 disclose in FIGS. 3 and 4, a casing for housing a final reduction gear for rear wheels and a wet multiple-disk braking device which is mounted in front of the final reduction gear in a direction of forward movement of a four-wheel vehicle. By mounting the wet multiple-disk brake in front of the final reduction gear, the wet multiple-disk braking device directly stops or brakes the rotation of the input shaft of the final reduction gear. The arrangement of the wet brake mounted in front of the final reduction gear, and the operation of directly stopping the rotation of the input shaft of the final reduction gear is complicated, limits design freedom and provides for inefficient braking of the rear wheels. In addition, if the gear fails in this structure, brake failure may occur resulting in the inability to slow or stop the rear wheels. Furthermore, the location of the rear gear case and location of the wet multiple-disk braking device which is mounted in front of the final reduction gear prevents minimization of the distance to the engine output.